In general, in the process of producing numerical data, which is obtained from the tracing of a model by stylus means and is used for in the subsequent cutting work, the profile of a model is continuously traced and the produced trace data is processed by means of calculation so that a numerical data for the subsequent cutting work is obtained. In view of the fact the precision of the cutting work is deteriorated when the cutting work is carried out using erroneous numerical data from the tracing of the model with a trace error, a prior art method of numerically controlled cutting work has been proposed in which the numerical data is corrected by the data corresponding to the error. This prior art method is described, for example, in Japanese Patent Publication No. 51-46311.
There is another problem in correcting the radius of the cross-section of a cutting tool. That is, when the radius of the cross-section of a cutting tool is different from that of a stylus, it is necessary to correct the value of the radius of the cutting tool and carry out the cutting work using said corrected value of the radius of the cutting tool.
To solve this problem, a prior art method of the correction of the radius of the cutting tool has been proposed in which the calculation of the value is conducted in the direction of the vector of the trace deflection and the correction of the radius of the cutting tool is carried out using the result of said calculating. However, it sometimes happens that an incorrect value of the trace deflection is obtained, and only the unidimensional trace deflection is obtained with the unidimensional tracer, and hence no direction is found for carrying out three dimensional correction. Under these circumstances, no correct calculation of the data can be carried out. Therefore, such prior art method does not provide a satisfactory solution of the problem.